This report describes the water resources of Genesee County, Mich., whose principal city is Flint. The sources of water available to the county are the Flint and Shiawassee Rivers and their tributaries, inland lakes, ground water, and Lake Huron. The withdrawal use of water in the county in 1958 amounted to about 45 mgd. Of this amount, 36 mgd was withdrawn from the Flint River by the Flint public water-supply system. The rest was supplied by wells. At present (1959) the Shiawassee River and its tributaries and the inland lakes are not used for water supply.

 Flint River water is used for domestic, industrial, and waste-dilution requirements in Flint. About 60 percent of the water supplied by the Flint public water system is used by Flint industry. At least 30 mgd of river water is needed for waste dilution in the Flint River during warm weather.

Water from Holloway Reservoir, which has a storage capacity of 5,760 million gallons, is used to supplement low flows in the Flint River to meet water-supply and waste-dilution requirements. About 650 million gallons in Kearsley Reservoir, on a Flint River tributary, is held in reserve for emergency use. Based on records for the lowest flows during the period 1930-52, the Flint River system, with the two reservoirs in operation, is capable of supplying about 60 mgd at Flint, less evaporation and seepage losses. The 1958 water demands exceeded this amount. Development of additional storage in the Flint River basin is unlikely because of lack of suitable storage sites. Plans are underway to supply Flint and most of Genesee County with water from Lake Huron.

The principal tributaries of the Flint River in and near Flint could furnish small supplies of water. Butternut Creek, with the largest flow of those studied, has an estimated firm yield of 0.054 mgd per sq mi for 95 percent of the time. The Shiawassee River at Byron is capable of supplying at least 29 mgd for 95 percent of the time.

Floods are a serious problem in Flint. The April 1947 flood, the largest on record, caused nearly $4 million flood damage in Flint. A proposed flood-control plan for Flint calls for channel, floodwall, and levee improvements and the removal or modification of some bridges.

Analyses of water samples taken from selected streams and lakes in the Flint area indicate that the waters are of the calcium bicarbonate type and generally hard to very hard. Flint River water is relatively uniform in quality although a progressive increase in iron, sodium, and chloride concentrations was noted between Otisville and Montrose. Downstream from Flint, the dissolved oxygen

content may be low during low flows. At times, concentrations of iron, manganese, phenols, color, and turbidity in Flint River water exceed the limits recommended in drinking water standards. Water temperatures ranged from freezing to 86°F in a 4-year period. The finished water supplied by the Flint water-treatment plant is fairly uniform in quality, moderately soft, alkaline, and low in color and turbidity. The pH is nearly always above 10. Further softening and removal of iron and related minerals would be desirable for certain industrial uses.

The quality of the water sampled in the Flint River tributaries was generally similar to that of the Flint River. However, no phenols or oils and waxes were found. Softening and other treatment dependent upon use would be required if these streams were developed for water supply.

Waters sampled in the Shiawassee River and selected lakes were generally less mineralized than Flint River water. Water from the lakes showed the lowest concentrations of dissolved solids. Softening would be required for nearly all uses. Additional treatment would depend upon contemplated use.

Shallow deposits of sand and gravel deposited as outwash along glacial meltwater streams and as deltas in the glacial lakes that covered the northwestern part of the county are sources of water to moderate- and large-capacity wells. Thick deposits of sand and gravel also fill some of the valleys in the bedrock surface and yield moderate to large supplies of water. Production from public supply wells tapping the drift aquifers in the area ranges from about 50 to 1,200 gpm. The water from the drift aquifer is hard or very hard and commonly contains objectionable amounts of iron.

The Saginaw formation is a source of water to wells supplying some of the small communities and industries in the county. The Saginaw, which is the uppermost bedrock formation in the area, underlies most of the county. It is composed of layers of sandstone, shale, and limestone and some beds of coal. The formation is composed principally of sandstone in some areas of the county, and shale in others. Production from wells tapping the Saginaw ranges from a few to about 500 gpm. The water produced is generally moderately hard or hard and commonly contains objectionable amounts of chloride. The quality of the water limits its development for water supply. Overdrafts from the Saginaw result in a lowering of the piezometric surface and commonly cause an upward migration of water high in chloride.

The Michigan and Marshall formations are generally not sources of fresh water where they are overlain by the Saginaw formation. In the southern and eastern parts of the county where they are overlain by glacial deposits, they are a source of water of good quality. The quantity of water obtainable from these formations is not fully known. However, the Marshall may be a source of large supplies of water in the southeastern part of the county.

An ample supply of water is available in lakes, ponds, and streams in the metropolitan area of Flint to meet requirements for domestic, sanitary, and firefighting use in civil defense emergencies. The extent of emergency use of water from these sources would depend upon the pumping, distribution, and treatment facilities available. Enough private industrial and commercial, and public wells are present in the area normally supplied by the Flint public water system to meet emergency requirements for domestic and sanitary use. Use of these wells would also depend upon available pumping and distribution facilities. Water from many of these wells contains objectionable amounts of chloride, but it could be used without treatment in an emergency.